Improvement in drafting-scales



UNrrn raras PATENT Enron.

IMPROVEMENT IN DRAFTlNG-SCALES.

Specification forming part of Letters Patent No. 38,904, dated Juue 16, 1863.

To all whom it may concern:

Be it known that I, J osIAH LYMAN, of Lenox, in the county of Berkshire and State of Massachusetts, have invented a new and useful instrument for drafting and plotting, and for all purposes in which distances are required to be measured, read, or laid down upon paper with accuracy.

To this instrument I apply the name of micrometer-scale,77 and l do hereby declare that the following is a full, clear, and exact description of the construction and operation of the same, reference being had to the accompanying drawings, and to the letters of reference marked thereon, making a part of this specification, in which- Figure 1 is a vertical and longitudinal section through the center of the entire instrument. Fig. 2 is a vertical view of the screwtube separa-te from the other parts of the instrument.V Figs.v3, 4, and 5 are transverse sections at the points a, b, and c, the parts all being in their normal position. Figs. 6, 7, and 8 are vertical views of the several sides of the scale-tube,v which is always triangular, as shown in Figs. 3, 4, 5, 9, or quadrangular. Fig. 9 is a vertical view of the instrument when resting upon its 'ortieth inch scale as base, showin g the spring attachment by means of which it is brought into contact with the rule of the protracting trigonometer patented May 15, 1860, (Additional Improvement No. 280,) and becomes a part of that instrument. These figures are all drawn in their true size and proportions, excepting that they represent one of the shorter classes of the instrument, the more convenient length for most uses being one foot for the graduated part.

To enable others skilled in the art to make and use my invention, I will proceed t0 describe speciically its construction and operation.

` The graduated or scale tube G T is composed of German silver, about one-twentieth of an inch thick, the width of the several sides of the tube in the triangular form,l as shown in Figs. 6, 7, and 8, being one inch, but in the quadrangular form about three-fourths of an inch, thesesizes being the least that will give the requisite strength to the tube and suflicient diameter to the micrometer-circle. For

most uses the triangular is preferable to the4 quadrangular form, since the former in reading and measuring distances presents itself to the eye at a much less oblique angle than the latter, and also admits of a perpendicular position to the prick 0r needle point in making a dot at the end of any required distance, though I claim both forms in the invention, and as equally applicable to the micrometer attachment herein described.

In the side of the scale Shown in Fig. 6 the units of division are tenths and'twentieths of a foot. In Fig. 7 the units are inches, halves,

and fourths of an inch. In Fig. 8 they are the same, and the subdivisions are duodecimal, but in Figs. 6 and 7 they are decimal.

vThe particular units of division represented in the drawings are not essential to the invention, but it is equally applicable to any units which its speciic use may require, especially the French centimeter and double centimeter.

The screw-tube S T, Figs. 1, 2, 3, 4., is made of bronze. lt isl indispensable that it should be so accurately tted to its bearing in the micrometer end piece M E, Figs. 1, 3, that it sh all have no perceptible pla-y, especially endwise. One of its essential peculiarities is, having a screw cut upon itsinterior extremity whose threads shall correspond in distance with the finest subdivisions of the coarsest scale-that is, (with the system of scales shown in the drawings,) two-hundredths of a foot. It is also essential that the interior extremity should be divided by two or three slots, as shown in Fig. 2, so as to give to it sprin g force, and hence a smooth, uniform friction, and ex` clude all play.

The end pieces ME and E, Figs. 1, 3, and 5,

are of German silver, and are permanently attached to the zero and scale tubes.

The xed nut F N, Fig. 1, is composed of German silver, and is permanently fastened to the scale-tube.

The micrometercircle M (seen in perspective in Figs; 6, 7, 8, 9, andin section in'Fig. 1) is compound, being composed ot' German silver externally, but internally of bronze, in order to secure smooth .friction in its contact with its bearing, the micrometer end pieceM E. Itis the same in form in all the three Figs. 6, 7, and8, but differently divided. 0f these circles there are as many as there are sides to the scale-tube, and they are exchangeable each for any of the others. That of Fig. 6 is divided into ten equal spaces, each subdivided into ve,

naking fifty subdivisions; that of Fig. 7 into awelve spaces, with sixty subdivisions; that of Fig. 8 into seventeen and twenty-eight onehundreths spaces, of which seventeen are equal, md are each subdivided into four, making sixty-eight subdivisions; but the remaining Jwenty eight one-hundredths of a space gives )ne subdivision and twelve one-hundredths, which, added to the former, makessiXty-nine md twelve one-hundredths subdivisions. The tirst two inches are so divided as to give decimal readings, the 'third so as to give a duodecimal reading. A circle divided to suit the French scale with the centimeter as' the unit and a :lecimal reading would require seventy-six onetifth subdivisions, very nearly. The circle may be divided to suit any unit of division or any number of subdivisions of the scale which its specific use may require.

The use of the micrometer, nut N, Figs. 1, 6, 7, 8, 9, is merely to hold the micrometer-circle tightly in its proper position against the smaller shoulder of the screw-tube, and for convenience in turning the former to any required distance or reading.

The object of the pin P, Fig. 1, inserted into the pin-orifice P O, Fig. 7, and passing into the screw-tube, is simply to hold the latter immovably in its normal position in exchanging one micrometer-circle for another.

The thumb-nut L at the other end of the scale-tube, Figs. l, 6, 7, 8, 9, while in the position indicated, serves merely for convenience in handling and sliding the scale; but when taken out and inserted into the outer extremity of the screw-tube at the micrometer end of the former it becomes a lengthening-piece, very essential when the instrument is used in connection with the trigonometer before referred to, for solving the problems of land-surveyin g.

The spring attachment Sp At, Fig. 9, is a piece of brass wire, bent as represented in the tgure, having two lips, one projecting downward and the other upward at the outer end of the double arm A A, by which this drafting scale becomes a sliding scale for the trigonometer, thus constituting apart of that instrument by taking the place of its scaleplate. ln using this attachment its extremities are inserted into two of the corresponding orifices at the ends of the scale-tube shown in Figs. l, 3, and 5. The scale is then placed in contact with one of the edges of the trigonometerrule, that side of its base thus in contact being elevated by the spring about the fortieth of an inch above the paper, while the opposite side rests upon it. By applying the finger to the upper lip, U L, which lies inward from the hither edge of the rule one-sixteenth of an inch or more, it is drawn toward the operator suiciently to allow the lower lip, L L, to slip over the said edge. If, now, a weight of one or two ounces be placed upon the arm A A, the instrument becomes a complete sliding scale, mathematically reliable. Besides, the scale can be readily transferred to the other side of the rule, or inverted, so that distances on its other border may be Yread or measured without removing from it the spring.

The operation or method of using this scale requires little explanation. Since the several sides of the scale-tube are graduated, while the zero-piece Z, Figs. 6, 7, 8, 9, is in close contact with it, whenever the two occupy relatively this position, each of the sides presents upon both its borders a double or triple scale divided into units and tenths or twelfths; and in laying down or measuring anydistance upon paper or elsewhere the zero-mark constitutes one of its terminal points, and the mark at the given or required number of units and tenths (sometimes half-tenths or quarter-tenths) the other. These marks either guide the eye with mathematical accuracy in sliding the scale to the proper position in any operation, or, with equal accuracy, the needle-point in making a dot.

To obtain hundredths and thousandths, or in measuring a distance embracing these additional portions of a unit, the micrometer-circle is turned toward the operator if held in the right hand, and from him if held in the left, till the required gure or mark in obtainin g or the required points on the paper in measuring a distance are reached, two of the numbered spaces making a hundredth of the coarser unit, and one of the subdivisions a thousandth of the same; but of the liner units, one of the numbered spaces making a hundredth, and each of the subdivisions making two-thousandths. This statement in respect to hundredths and thousandths, however, supposes the graduations of any side of the instrument to embrace but two units of division-viz., the tenth of a foot and its half; the inch and its half 5 the centimeter and its double unit. But in scale Fig. 7 there are thee units of division--viz inches, halves, and fourths; hence in using the nest subdivisions of this scale the numbered spaces of the micrometer-circle equal two-hundredths, and each subdiviions four-thousandths. Moreover, in scale Fig. 8 there are the same three units of division as in scale Fig. 7, and each is subdivided, or supposed to be, into twelftlis of the unit, thus rendering them duodecimal. The corresponding micrometer-circle also being duodecimal in its numbered spaces, and each of them being subdivided into four equal parts, the micrometerreading gives one hundred and forty-fourths and ve hundred and seventy-sixths, two hundred and eighty-eighths and eleven hundred and fifty-seconds, ve hundred and seventy-sixths and twenty-three hundred and fourths of an inch. Besides, it is manifest that the subdivisions of the micrometer-circle can be themselves subdivided by the eye, so as easily to allow of a reading equal to the tenth part of eachthat is, one hundred-thousan'dths of a foot in scale Fig. 6, and ten-thousandths of an inch in scale Fig. 7. lI his is, however, carrying the reading of the several scales to a nicety, somewhat beyond the power of thc best marking-machine to divide. Still, it. is safe to say that this power may extend to the twenty-five hundredth part of an inch. But

readily applied to a boxwood in place of a metallic scale, though, on account ofthe tendency of the former to spring and shrink, the latter the principle involved in the invention, withis preferable.

out any mechanical interference, will extend with equal certainty to the fourth part of this last space; hence it may be truly stated that when this micrometer-scale is used in connection with the protracting trigonometer before referred to a line twelve inches long may be laid down or measured reliably to the thirtythousandth part of its length, which is equivalent to about a foot in the distance of ve and seven-tenths miles. This degree of accuracy, however, supposes the use of the microscope, and n0 perceptible error in any of the manipulations of the instrumentan attainment acquired only by practice and skill. Still, ordinary skill will be reliable to the ten or twelve thousandth part of a foot, and unusual skill will nd full scope in the simplicity, convenience, perfection, and extent of the invention.

By inserting into the micrometer end piece M E, Figs. l and 3, near the several corners, three brass pins one-tenth inch in diameter for the triangular or four for the quadrangular form, instead of the sliding tube, the micrometer attachment herein described may be What I claim as my invention isl. The combination and arrangement, in the manner described and for the purposes set forth, of a triangular or quadrangular scale with a screw-micrometer, by which distances on paper or otherwise may be measured, read, 0r laid down with mathematical precision.

2. rPhe arrangement, as set forth, for exchanging one micrometer-circle for another suited to any one of the several scales.

3. The peculiar arrangement of the screwtube, by which a smooth, uniform friction is given to its action, and all perceptible error from play or other causes is excluded from the readings of the micrometer-circle.

4. The arrangement, as set forth, of the spring attachment, by which this draftingscale may be brought into connection with and become a part of the protracting trigonometer.

JOSIAH LYMAN. Witnesses:

WM. S. TUCKER, ALBERT J. LYMAN. 

